验证码的实现
作者：互联网
验证码的实现需要用到session技术，就先说说session是干什么的吧
Session技术是将数据存储在服务器端的技术，会为每个客户端都创建一块内存空间 存储客户的数据，但客户端需要每次都携带一个标识ID去服务器中寻找属于自己的内 存空间。所以说Session的实现是基于Cookie，Session需要借助于Cookie存储客 户的唯一性标识JSESSIONID （Cookie技术是将用户的数据存储到客户端的技术）
Session技术：存到服务器端 借助cookie存储JSESSIONID
HttpSession session = request.getSession();
session.setAttribute(name,value); //将值value 他的名字是name 存储到session中
session.getAttribute(name); //获取name（上边的名为name的东西）
session生命周期
创建：第一次指定request.getSession();
销毁：服务器关闭、session失效/过期、手动session.invalidate();
session作用范围：默认一会话中
下面开始验证码的实现
首先需要一个jar包 itcast-tools-1.4.2.jar
需要的在这里领就行
链接: https://pan.baidu.com/s/1zE74X9sGCmw14sSdbuWTig 提取码: zew5 复制这段内容后打开百度网盘手机App，操作更方便哦
先是jsp页面
1 <%@ page language="java" contentType="text/html; charset=UTF-8"
2 pageEncoding="UTF-8" import="java.util.*"%>
3 <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
4 <!DOCTYPE html>
5 <html>
6 <head>
7 <meta charset="UTF-8">
8 <title>Insert title here</title>
9 <meta http-equiv="pragma" content="no-cache">
10 <meta http-equiv="cache-control" content="no-cache">
11 <meta http-equiv="expires" content="0">
12 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
13 <meta http-equiv="description" content="This is my page">
14 <script type="text/javascript">
15 function _hyz() {
16 /*
17 1. 获取<img>元素
18 2. 给它的src指向为/tools/VerifyCodeServlet
19 */
20 var img = document.getElementById("imgVerifyCode");
21 // 需要给出一个参数，这个参数每次都不同，这样才能干掉浏览器缓存！
22 img.src = "/TestDenglu/VerifyCodeServlet?a=" + new Date().getTime();
23 }
24 </script>
25 </head>
26 <body>
27 <%--
28 1. 写表单，其中包含图片（验证码）
29 2. 让图片显示出来：
30 把<img>的src指向VerifyCodeServlet，你需要在web.xml中部署VerfiyCodeServlet
31 3. 换一张
32 --%>
33 <div style="color: red"><%=request.getAttribute("loginInfo")==null?"":request.getAttribute("loginInfo") %></div>
34 <form action="/TestDenglu/LoginServlet?method=checkCode" method="post">
35
36 <input type="hidden" name="method" value="login">
37 用户名：<input type="text" name="username" /><br />
38 密 码：<input type="password" name="password" /><br />
39 验证码：<input type="text" name="verifyCode" /><br />
40 <img src="/TestDenglu/VerifyCodeServlet" id="imgVerifyCode" /> <a
41 href="javascript:_hyz()">换一张</a> <br />
42 <input type="submit" value="提交" />
43 </form>
（其中的TestDenglu是我的项目名）
web.xml部署
<servlet>
<servlet-name>VerifyCodeServlet</servlet-name>
<servlet-class>cn.itcast.vcode.servlet.VerifyCodeServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>VerifyCodeServlet</servlet-name>
<url-pattern>/VerifyCodeServlet</url-pattern>
</servlet-mapping>
LoginServlet
1 package com.jdbc.servlet;
2
3 import java.io.IOException;
4 import java.io.PrintWriter;
5
6 import javax.servlet.ServletException;
7 import javax.servlet.annotation.WebServlet;
8 import javax.servlet.http.HttpServlet;
9 import javax.servlet.http.HttpServletRequest;
10 import javax.servlet.http.HttpServletResponse;
11
12 import com.jdbc.dao.UserDao;
13
14 /**
15 * Servlet implementation class LoginServlet
16 */
17 @WebServlet("/LoginServlet")
18 public class LoginServlet extends HttpServlet {
19 private static final long serialVersionUID = 1L;
20
21 /**
22 * @see HttpServlet#HttpServlet()
23 */
24 public LoginServlet() {
25 super();
26 // TODO Auto-generated constructor stub
27 }
28
29 /**
30 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
31 * response)
32 */
33 protected void doGet(HttpServletRequest request, HttpServletResponse response)
34 throws ServletException, IOException {
35 // TODO Auto-generated method stub
36 response.setContentType("text/html;charset=UTF-8");
37 request.setCharacterEncoding("UTF-8");
38
39 String method = request.getParameter("method");
40 if(method.equals("checkCode"))
41 {
42 checkCode(request,response);
43 }
44
45 }
46
47 public void checkCode(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
48 request.setCharacterEncoding("UTF-8");
49
50 String checkCode_client = request.getParameter("verifyCode");
51 // VerifyCodeServlet会把真正的验证码保存到session中
52 String checkCode_session = (String) request.getSession().getAttribute("vCode");
53
54 if(!checkCode_session.equals(checkCode_client)) {
55 request.setAttribute("loginInfo", "您输入的验证码不正确");
56 request.getRequestDispatcher("/form.jsp").forward(request, response);
57 return;
58 }
59 if(checkCode_session.equals(checkCode_client)) {
60 request.setCharacterEncoding("utf-8");
61 response.setContentType("text/html;charset=utf-8");
62 String username = request.getParameter("username");
63 String password = request.getParameter("password");
64 String psw =new UserDao().findUsername(username);
65
66 //request.getSession().setAttribute("loginInfo", username);
67
68 if(psw ==null){
69 PrintWriter out = response.getWriter();
70 out.println(" <script type='text/javascript'> alert('该用户不存在');window.location.href='login.jsp'</script>");
71 out.println("</HTML>");
72 out.flush();
73 out.close();
74 }
75 if(psw!=null&&!psw.equals(password)){
76 PrintWriter out = response.getWriter();
77 out.println(" <script type='text/javascript'> alert('密码错误，请重新录入');window.location.href='login.jsp'</script>");
78 out.println("</HTML>");
79 out.flush();
80 out.close();
81 }
82 if(psw!=null&&psw.equals(password)){
83 PrintWriter out = response.getWriter();
84 out.println(" <script type='text/javascript'> alert('登陆成功！');window.location.href='welcome.jsp'</script>");
85 out.println("</HTML>");
86 out.flush();
87 out.close();
88 out.print(true);
89 }
90 }
91
92 }
93
94
95
96 /**
97 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
98 * response)
99 */
100 protected void doPost(HttpServletRequest request, HttpServletResponse response)
101 throws ServletException, IOException {
102 // TODO Auto-generated method stub
103 doGet(request, response);
104 }
105
106 }
标签：checkCode,实现,request,验证码,session,import,response,out 来源： https://www.cnblogs.com/022414ls/p/12388449.html